(1) Field of the Invention
The present invention relates to the use of withanolides as selective cyclooxygenase-2 (COX-2) inhibitors. The withanolides have little effect on COX-1.
(2) Description of Related Art
Withania somnifera (L) Dunal of solanaceae, is an erect evergreen shrub distributed throughout the drier parts of India. W. somnifera, known as Aswagandha, is well known for its use in Ayurvedic medicine. The Aswagandha root extract was reported as a folk remedy for adenopathy, arthritis, asthma, hypertension, inflammations, and rheumatism (Thakur, R. S., et al., Major medicinal plants of India; Ed.; Central Institute of Medicinal and Aromatic Plants: Lucknow, India, 531 (1989)). The leaves of W. somnifera were also used as a cure for several illnesses including tumors, inflammations, conjunctivitis and tuberculosis (Thakur, R. S., et al., Major medicinal plants of India; Ed.; Central Institute of Medicinal and Aromatic Plants: Lucknow, India, 531 (1989)). Currently, powdered roots or root extract of this plant are used as a dietary supplement in the United States.
The major chemical constituents reported from W. somnifera are called withanolides. These compounds are structurally diverse steroidal compounds with an ergosterol skeleton in which C-22 and C-26 are oxidized to form a δ-lactone; (Ray, A. B., et al., Prog. Chem. Org. Nat. Prod. 63, 1-106 (1994)). The chemical investigations of the roots and leaves of W. somnifera resulted in the isolation and characterization of several withanolides (Matsuda, M., et al., Bioorg. Med. Chem. 9, 1499-1507 (2001)). The fruits of this plant are tiny orange berries and reported to contain saturated and unsaturated fatty acids (Stoller E. W., et al., Lloydia, 37, 309-312 (1974); Monika, P., et al., Asian J. Chem. 6, 442-444 (1994); and Monika, P., et al., Wsci. Phys. Sci. 5, 81-83 (1993)). However, leaves and fruits are not fully investigated for biological activities. The withanolides are classified according to their structural skeleton (Ray, A. B., et al., Prog. Chem. Org. Nat. Prod. 63, 1-106 (1994)) and the structural variation is responsible for the wide array of pharmacological activities. Withanolides have been studied for their anti-inflammatory, antitumor, cytotoxic, immunomodulating activities and for the protection against CCl4-induced hepatotoxicity (Ray, A. B., et al., Prog. Chem. Org. Nat. Prod. 63, 1-106 (1994); and Anjaneyulu, A. S. R., et al., Studies in Natural Products Chemistry: Structure and Chemistry (Part F); Ed. Atta-ur-Rahman, Vol. 20, 135-261 (1998)). They were also reported to induce phase-II enzymes in animal models, which is considered to be one of the mechanisms in cancer chemoprevention (Misico, R. I., et al., J. Nat. Prod. 65, 677-680 (2002); and Su, B. N., et al., Tetrahedron 58, 3453-3466 (2002)).
Cyclooxygenase-1 (COX-1) and -2 (COX-2) enzymes are responsible for the conversion of arachidonic acid, a lipid present in the cell, to prostaglandins. Prostaglandins in turn cause inflammatory responses in the body. Inhibition of COX-1 enzyme may result in the formation of ulcers in many human and hence the selective inhibition of COX-2 enzyme by compounds has a major advantage over non-selective nonsteroidal anti-inflammatory drug (NSAIDs) (Smith, W. L., et al., Anu. Rev. Biochem. 69:145-182 (2000)) sold over the counter (OTC). It is important to note that over expression of COX-2 enzyme was observed not only in inflamed cells but also by various types of tumor cells (Patti, R., et al., Cancer Lett. 180:13-21 (2002); Ohno, R., et al., Cancer 91:1876-1881 (2001); and Khuder, S. A., et al., British Journal of Cancer 84:1188-1192 (2001)). Hence, COX-2 inhibitors with little or no COX-1 activity are of great interest for the chemoprevention of cancer.